Method of liquefying and storing fuel gases



A 1 S. TWOMEY 2,090,163

METHOD OF LIQUEFYING AND STORING FUEL GASES Fil ed May 9, 1954' LEE- 5. TWOMEY NVNTOR AT RNEY Patented Aug. 17, 1937 UNITED STATES METHOD OF LIQUEFYING AND STORING FUEL GASES Lee S. Twomey, Vista; Calif.

Application May 9, 1934, Serial No. 724,692

6 Claims.

The object of my invention is to provide means and a method for economically reducing hydrocarbon gases to the liquid condition, for maintaining them in storage at a slight superatmospheric pressure, and for converting them back to the gaseous state at such times as they may be required.

It is well known that at the present time many large cities rely largely on gas for household heating and for industrial purposes and that this gas is in large part of natural origin and is brought to the point of consumption over great distances. The pipe lines through which this gas is conducted, often hundreds of miles in length, are enormously costly to build and to operate. The

demand for gas naturally fluctuates with weather 1 conditions, the variation between peak load and low load being in many cases as high as ten to one. As it is commercially impossible to provide an adequate amount of storage for gas at atmospheric temperature and pressure, or even for gas compressed to a fraction of its original volume, it has been necessary to adopt one or the other of two alternatives: either to provide production,

pipe lines, and pumping facilities having a normal capacity adequate for normal loads, crowding these lines to their limit during times of peak load and often leaving an excess demand un- 30 supplied, or to so proportion the production and transportation facilities as to provide for maximum load, with the result that a very large investment is standing idle the greater part of the time.

Further, in most oil fields gas flow is utilized as a means for producing or is concomitant with the production of petroleum, and as the daily output of wellsis limited by law or agreement and the wastage of gas is forbidden, a reduction in 4 the demand for gas often results in a direct loss of allowable oil production. From the standpoint of the oil producer it is highly desirable that the requirement for gas be the same throughout the seasons.

r, My proposal is to operate pipe lines conducting gas in the most economical manner, at their normal load constantly maintained, to reduce the excess delivery during periods of low load to the liquid form, to maintain this liquefied gas in to storage at substantially atmospheric pressure, and to draw on this liquid storage during peak load periods. By this procedure, which is made possible by the methods herein disclosed, existing lines may be made to transport much greater 5;, quantities of gas throughout the rotation of seasons than is now possible, the excessive cost of pumping at maximum pressure during peak load periods is avoided as is also acute shortage during times of extreme cold, and new installations of pipe lines and pumps may be based on average annual loads rather than on the maximum seasonal load.

It is now common practice to store limited quantities of fuel gas in pressure vessels, at from 100 to 500 pounds gauge. When it is reflected that any unit of space will hold approximately eight volumes of gas compressed to 100 pounds gauge or thirty five volumes compressed to 500 pounds, while, it will hold approximately six hundred and forty volumes of the same gas when reduced to liquid form, and further that the liquid gas does not necessarily require the use of pressure vessels, the extreme advantages incident to storage in the liquid phase will be evident.

Natural gas, while quite variable in the proportions of its constituents, is qualitatively constant, being composed in almost all cases of varying proportions of the first four members of the normal series of parafins-methane, ethane, propane, and butane. The pentanes and other constituents which may profitably be put into commercial liquid products are now, as a rule, closely fractionated from the constituents normally gaseous, and sold with the gasoline which accompanies most gas produced from oil wells.

The temperatures and pressures at which hydrocarbon fuel gases may be liquefied will vary from place to place and from time to time with the quantitative composition of the gas delivered by any pipe line. The plant in which it is reduced to the liquid state must therefore be reasonably flexible as to both temperature and pressure possibilities, but should in any case be capable of liquefying pure methane, which is the most refractory constitutent of most natural gases. The required plant will have apparatus for liquefying and suitable vessels for storage without waste, the latter being provided with means for withdrawing the liquid and for reconverting' it to the gaseous form without fractionating it by evaporation of its lighter constituents.

The method steps making up my invention are best described in connection with the attached drawing, which diagrammatically illustrates various combinations of apparatus suitable for putting them into efiect.

In the following description all temperatures are in degrees Kelvin, or centigrade degrees absolute. Pressures stated in atmospheres are absolute, those given in pounds gauge are plus atmospheric absolute.

Referring to the drawing: I0 is a receiver containing a quantity of liquefied anhydrous ammonia, at atmospheric temperature and under a pressure equivalent to its vapor pressure at that temperature. -The liquid ammonia passes through pipe I I and a regulating valve l2 to the shell (the space surrounding the tubes) of a condenser IS, the shell being maintained at or about atmospheric pressure by regulation of the valve. In this shell the ammonia vaporizes at an initial temperature about 240, being its boiling point at atmospheric pressure. Absorbing heat from gaseous ethylene flowing downwardly through the tubes of condenser IS, the ammonia gas leaves the shell through pipe M at substantially atmospheric temperature. Passing then to compressor l5, it is raised to its condensation pressure at atmospheric temperature, then through pipe l6 to and through the tubes of a condenser l1, these tubes being cooled by water. In the condenser it is brought back to substantially atmospheric temperature and thereby condensed, the liquefied ammonia passing through pipe l8 to receiver III. This completes a closed ammonia cycle.

Numeral l9 indicates a receiver containing a quantity of liquefied ethylene, at a temperature about 240 and at a pressure corresponding to its vapor pressure at that temperature. The liquid ethylene passes through pipe 20 and a regulating valve 2| to the shell of a condenser 22, the shell being maintained at or about atmospheric pressure by regulation of the valve. In this shell the ethylene vaporizes at an initial temperature about 168, being its boiling point at atmospheric pressure.

Withdrawing heat from partly cooled fuel gas flowing downwardly through the tubes of condenser 22, the gaseous ethylene leaves the shell through pipe 23 at substantially atmospheric pressure and flows to a group of the tubes of a dehydrating'interchanger 24 in which it is heated to atmospheric temperature in cooling compressed fuel gas.

' Passing then through pipe 25 to compressor 26 it is raised to its condensation pressure at the temperature of the ammonia cooled tubes of condenser l3. From the compressor the hot compressed gas fiows through pipe 21 and the tubes of a cooler 28 which is supplied with cold water. In cooler 28 the compressed gas is returned 'to atmospheric temperature but is not one liquefied, the compressed and cooled gas flowing through pipe 29 and the tubes of condenser i3 which, as already stated, are cooled by evaporating ammonia to 240. At this temperature the ethylene condenses and passes through pipe 30 to receiver l9, thus completing the ethylene cycle.

A continuous stream of the fuel gas to be liquefied is introduced to the system through a pipe 3|, which may be the pipe line through which gas is brought from the field and which may extend to connect with the distribution system as a pipe 32, a regulating valve 33 being interposed to maintain a substantially constant but usually slight pressure in the intake pipe 34. Thispipe conducts the gas stream to the suction side of a compressor 35 by which it is raised to a pressure at which it will condense at a temperature of 168. The hot compressed gas passes through pipe 36 and the tubes of a cooler 31 which is supplied with cold water. In this cooler the compressed gas is returned to atmospheric temperature but is not liquefied, the compressed and cooled gas flowing through pipe 38 either to'the shell of a dehydrating interchangeror to a device for scrubbing out the major part 01' any carbon dioxide which may be present in the fuel gas.

The scrubber consists of a tower 39 arranged to collect a, pool of water 40 in its lower end. A pump 4| draws a stream of this water through pipe 42 and discharges it through pipe 43 into the lower end of a tubular interchanger 44. A chamber 45 above the upper tube sheet in the tower permits the escape of carbon dioxide evolved from the saturated water when it is heated as by a steam coil 46. A vent valve 41 permits the escape of this gas when it reaches system pressure. A float valve 48 governs the height of the water pool 49 and permits a stream of hot water to pass through pipe 50 to the upper end of the space around the tubes. Passing downwardly through the shell the hot water counterfiows the upfiowing cold water within the tubes and passes through pipe 5| to a hose nozzle or other spraying means 52 at atmospheric temperature and at system pressure.

The gas leaving cooler 31 through pipe 38 enters the bottom of the spray tower and flows upward in counterfiow to the descending water streams and passes from the upper end of the tower through pipe 53 to dehydrating interchanger 24. To bypass the scrubbing unit in case its use should not be necessary or desirable a crossover pipe 54 and diversion valves 55 and 56 are provided.

In this interchanger the fuel gas is cooled, by

, cold ethylene gas and by gas returned from farther on in the system, to a temperature at which water vapor is condensed and in large part frozen. It should be provided with baffles 51 by which it is divided into pockets, these pockets being drained by valves 58. The entire unit should be duplicated and provided with suitable diversion pipes and valves so that one may be cut out 01' the system and freed from ice while the other is being used.

From the dehydrator the partly cooled gas passes through pipe 59 into the tubes of condenser 22 .which, as said, are cooled by liquid ethylene evaporating at atmospheric pressure at 168 K. In this condenser the entire gas liquefies unless it contains hydrogen or nitrogen which, if present, may be separated in later elements of the apparatus. Any carbon dioxide which may be present in the original gas and is not removed in the scrubber is frozen at the temperature existing in this condenser but is not deposited in the tubes because of the rapid flow of liquid hydrocarbons over them, and the entire condenser output, consisting of liquid hydrocarbons, suspended solid carbon dioxide, and gaseous nitrogen and hydrogen, passes through pipe 6| to the trap 62. The trap which, like the dehydrator, should be provided in duplicate to permit 01 thawing when choked, is a vertically arranged shell into which pipe 6| enters ata medial height. Above this level a filtering disc 63 is disposed across the shell, this disc being of cloth supported by a perforated plate or of fine mesh metal filter cloth or other known filtering material. Carbon dioxide crystals entering with the liquefied gas may settle into the lower part of the shell from which they may be withdrawn as a slimy suspension through valve 64, or they may pass upwardly with the liquidand be retained by the .screen. The liquid and gaseous portions of the stream pass through the screen and through pipe 86 to the tubes of an interchanger 86.

The pressure in the various receivers, using the refrigerating gases above described will be approidmately 110 pounds gauge in ammonia receiver l and approximately 250 pounds gauge in ethylene receiver I9. The pressure in thetrap will vary with the constitution of the particular gas, but it we assume the gas to consist entirely of methane, which is an extreme condition, it will be about 290 pounds gauge. With most natural gases the pressure will ,be materially lower. All the above temperatures assume perieet interchange, which is hardly realized, and in practice the outlet temperatures will usually be about above those stated.

The above described method of cooling and liquefying gases is substantially that described and claimed in my copending application entitled Method of producing low temperature refrigeration", filed May 9, 1934, under Serial No. 724,691.

As fully set forth in the copending application,

' any one of a number of other gases may be substituted for ammonia in the first cycle, as for example propylene, propane, allylene, methyl chloride, sulphur dioxide, and carbon dioxide, while ethane and nitrous oxide may be substituted for ethylene in the second, all these changes involving some changes in temperatures and pressures. It is also possible to raise and lower the evaporating temperatures of the refrigerant gases by varying the pressure to which they are expanded. Air cooled apparatus may be substituted for the water cooled units i9, 32, and 4H, and other changes in structure and operation may be made without departing from the spirit of the disclosure.

As above described, the product (liquefied fuel gas) continuously passes into trap 62 at a temperature approximating 168 absolute and a pressure ranging downward from 290 pounds gauge. As it would be unduly expensive to store the liquid under such conditions of temperature and pressure, I first reduce its temperature to that at which its Vapor pressure is only slightly superatmospheric, preferably not in excess of pounds gauge. If the liquid fuel gas should consist solely of methane, the temperature at 15 pounds gauge would be 122, but in practice it will usually be somewhat higher.

To accomplish this result I permit a portion of the liquefied gas to evaporate and expand either to atmospheric pressure, at which pressure methane will be reduced to 112, or to the pressure at which it is to be stored.

The liquid and gaseous products fiow together from the trap through pipe 65 and the tubes of an interchanger 66, in which its temperature is I somewhat reduced as will be described. Thence the liquid fiows through pipe Bl and valve 68, by which the pressure is reduced, into a storage tank 69 so proportioned as to have a safe working pressure of say 15 pounds gauge. This tank should be provided with a blow-off pipe it! having a safety valve Ti set for a pound or two over working pressure, but this valve is provided for emergencies only.

The pressure on this tank may be read on a pressure gauge 12 and should be maintained at the working pressure by manipulation of a valve 13 in a return gas line 14. This valve may conveniently be a weighted or spring relief valve set for the working pressure.

On the passage of the liquid product through control valve 68 into the zone of lower pressure within storage tank 69 a portion or the liquid-will flash into the gaseous form and the temperature will be reduced to the boiling point of the-liqparts 01' this apparatus which are materially below atmospheric temperature are heavily heat in sulated, but as this practice is entirely conventional, it need not be described in detail.

It should be observed that the tank pressure of 15 pounds above mentioned is suggestive only, being a rather desirable mean between the very low temperature required to maintain the liquid stable at atmospheric temperature and the heavy apparatus required to store at compression pressure. It will be obvious, however, that a large part of the advantages of the lnvention-would accrue to the use of any presure within the limits of the compression, provided always that the temperature maintained in the storage vessel be below the critical temperature of the liquid and not substantially above the boiling point of the liquid at whatever pressure may be applied.,.

The gas produced by the above described fiashing operation leaves the tank through pipe 14, at the temperature of the liquid in the tank, and is thus materially colder than the fluids passing through interchanger 662' To recover the cooling 14 to the shellof interchanger 66 where it somewhat reduces the temperature of the fluid stream leaving trap 62, then through pipe 15 to one of the tube groups of the dehydrating interchanger 24, where it is brought back to atmospheric temperature, and finally returns through pipes H and 34 to the intake side of the fuel gas compressor. If this vent gas contains any material proportion of hydrogen or nitrogen, it may be preferable to return it to distribution pipe 32 through crossover pipe 18, diversion valves 19 and Bil being provided for that purpose.

The liquefied fuel gas being new in storage at a preferred superatmospheric pressure and at a temperature at which its vapor pressure does not exceed the preferred storage pressure, it is necessary to maintain it at that temperature so long as it is stored, and as even the most effective in sulation will permit some infiltration of atmospheric heat toward the storage vessel, it becomes necessary to constantly withdraw this heat either from the stored contents or from a fluid layer interposed between the vessel itself and the interior of the insulation.

The first of these alternatives is shown in the drawing as a. pipe coil 86 sealed into. the upper portion of the vessel and supplied with a liquefied gas suchas methane. is maintained at a pressure below that of the liquefied refrigerant and the evaporation of this liquid as it is admitted through control valve 82 reduces the temperature of the coil below the temperature of the stored liquid and thus provides for absorption of the heat which passes through the insulating layer into the liquefied contents of the vessel. The supply of liquid is shown as being drawn through a pipe 83 from a source of liquid of the same or lower boiling point, which will be v described.

The interior of the coil and spaced a few inches from it, this jacketbeing gas tight at atmospheric pressure. The liquefied cooling gas is admitted to this jacket through a valve 85, in such quantity as to maintain at least a small pool of liquid in the jacket, which is maintained at atmospheric pressure. This liquefied gas is regasifled at a rate determined by the rate of heat infiltration, and maintains around the vessel a temperature slightly below the normal storage temperature, thus preventing atmospheric heat from reaching the stored contents. The gas thus produced in either the coil or the jacket passes through pipe 88 into the system by which it is produced, to be reliquefied. While not functionally identical, these two methods for maintaining the stored liquids ata stable temperature are practically equivalent.

and methane, 95, 96, and 91 are water cooled condensers for removing the heat of compression from the same gases, and 98, 99, and I88 are interchangers. The liquid methane collecting in receiver89 passes through interchanger I88 and thence through pipe 83 to valve 82 through which it is admitted to the expansion coil 8i or to valve by which it is admitted to jacket 84. In either case the expanded gas returns to the suction side of compressor 94 through pipe 88 to methane interchanger I88, then through pipe I8I to ethylene interchanger 99, through pipe I82 to ammonia interchanger 98 and finally through pipe'l83 to the suction of methane compressor 94, at substantially atmospheric temperature and pressure.

The object in maintaining even a slight superatmospheric pressure on tank 52 is to provide a heat head between the contents of the tank and a liquid of the same boiling point expanding to atmospheric pressure. By expanding the cooling liquid to a slightly subatmospheric pressure, or by using a cooling liquid of lower boiling point, the requirement for pressure on the tank contents may be avoided.

On the other hand it may be economically desirable to store the liquid product at much higher pressures, as from 100 pounds to 400 pounds gauge, in which case the initial pressure on the gas is increased and the condensing temperature is correspondingly raised. At 100 pounds gauge the boiling point of methane is 142 K., at 400 pounds it is 171 K., and at these temperatures the heat head between the atmosphere and the contents of the tank is materially lowered, with a consequent reduction in the amount of refrigeration required to maintain a constant temperature within the tank. At 400 pounds pressurethe cooling may be effected by the atmospheric pressure evaporation of liquid ethylene.

In returning stored gas into the distribution.

system it is necessary to supply the heat rendered latent in evaporation and for returning the gas to atmospheric temperature. For this purpose a device is provided comprising a shell I89 into which liquefied gas passes from storage vessel 89 through pipe I84 controlled by a valve I85, the gasified material flowing from the upper part of the shell through pipe I88 into distribution pipe 32. If the pressure in the tank is below tilt of distribution, the liquid'may be pumped ini the gasifylng device. The requisite heat is sur plied by steam or other heating fluidadm'itted t the space around the tubes through a pipe an valve I81 and the space may be drained by mean of a pipe and valve I88.

I claim as my invention:

1. The method of liquefying and storing hydr carbon fuel gas which comprises: raising a stream of said fuel gas to a material superatmospheri pressure; eflecting a first cooling 01 said fuel ga stream to substantially atmospheric temperature eilecting a second cooling of said stream to 1 temperature below the freezing point of wate whereby said stream is substantially. dehydrated effecting a third cooling of said stream by hea interchange against an evaporating liquid rei'rig erant to a temperature at whlch the hydrocar' bon constituents thereof are liquefied "at com pression pressure; effecting a fourth coolingo said stream; introducing said stream into a storage vessel maintained at a desired subatmos pheric temperature, and passing any fuel ga: evolved in said vessel in heat exchange relatior with said stream successively through said i'ourtt and second cooling effects.

2. In the storage of liquefied hydrocarbon i'ueI gases at temperatures materially below atmospheric-the step of evaporating a liquid refrigerant in heat interchange relation with said liquefied hydrocarbon in a zone substantially surrounding a stored body of said liquefied hydrocarbon, and circulating and reliquefying said refrigerant in a closed cycle.

3. In the production and use of liquid methane as a refrigerant, the steps comprising: liqueiying a stream of compressed gaseous methane by heat interchange against a stream of evaporating liquid ethylene; liquefying said ethylene stream under pressure by heat interchange against a stream of evaporating anhydrous liquid ammonia; liquefying said ammonia stream by cooling under superatmospheric pressure, evaporating said liquid methane stream under less than its compression pressure in heat exchange relation with an object to be cooled; passing the evaporated methane in heat exchange relation successively against said liquid methane, ethylene, and ammonia streams, whereby said streams are cooled below their respective liquefying temperatures, and returning the gaseous methane at substantially atmospheric temperature to be recompressed.

4. The method of introducing a stream of liquefled gas under pressure into a storage vessel maintained at a lower pressure which includes the step of cooling said stream to a temperature of stability at vessel pressure by the partial evaporation of said stream on the introduction of said stream into said vessel and by heat interchange between said stream while at compression pressure and the cold gases produced by said evaporation.

5. In the storage of liquefied hydrocarbon fuel gases at temperatures materially below atmospheric, the steps comprising: evaporating liquid methane in heat interchange relation with said liquefied hydrocarbon; circulating and reliqueiying .a stream of said methane in a closed cycle by compression and heat interchange of said methane against a stream of evaporating liquid ethylene; liqueiying said ethylene stream under pressure by heat interchange against a stream 4 of evaporating anhydrous liquid ammonia; liquefying said ammonia stream by cooling under superatmospheric pressure, and cooling each of said streams to a point below its liquefying temperature and after liquefaction by heat interchange against a stream of said evaporated methane.

6. The method of transmitting and distributing a fuel gas which comprises: liquefying the portion of the gas delivered through the transmitting line in excess of the momentary demand of the distributing system for said gas; storing said liquefied gas in the liquid condition; gasifying said liquefied gas at times of increased demand, and delivering said gas to the distributing system.

LEE S. TWOMEY. 

